Heaters are typically used in temporary applications, such as construction sites, as a temporary heat source before a primary and permanent heat source is functional and usable or for example for heating event tents. Traditionally, most heaters for this type of application comprise a burner inside a tubular housing, with a fan behind the burner blowing air around the burner and out of the end of the heater. This is known as a direct-fired heater in that the combustion gases flow directly into the heated space. There are also indirect-fired construction heaters that incorporate a heat exchanger to permit the venting of combustion gases out of the heated space. Indirect-fired heaters are inherently less efficient in that a portion of the heat is normally lost through the exhaust. Indirect-fired heaters are also inherently larger because they require a heat exchanger and therefore a larger cross-section to handle the airflow.
Most construction heaters that are used with ductwork are of the indirect-fired type. The main reason for this is that the variation in airflow when a heater is ducted can significantly impact the quality of combustion in a direct-fired heater, leading to increases in harmful emissions such as carbon monoxide. This is because of the increase in backpressure inherent with the attachment of ductwork to the heater. Heaters used in temporary applications must be able to function safely within the full range of installations in which they may be employed.
Due to the high operating temperatures inherent to heaters, the operational lifetime of various components, such as the burner, gas lines, the walls of the combustion chamber, etc., tend be short unless higher grade or heavier materials are used.
A need therefore exists to provide a direct-fired heater suitable for use with ductwork that overcomes one or more of the shortcomings outlined above or in the art.